Rivers around the world show "worrying levels of ecosystem degradation", according to a study led by University of Coimbra (UC) researcher Maria João Feio, which was released today.

The results of the study show "worrying levels of degradation in riverine ecosystems, with less than half of the stretches studied in good biological quality (42 to 50%, depending on the biological element - fish or invertebrates) and around 30% severely degraded," said Maria João Feio.

According to the scientist from the Center for Marine and Environmental Sciences and the UC Faculty of Science and Technology, "the worst conditions were found in arid and equatorial climates".

This study brought together three dozen researchers from around the world and aimed to analyze the biological state of rivers as broadly as possible, based on two bioindicators used in river monitoring: benthic macroinvertebrates and fish.

Results from monitoring programs in 45 countries (64 study regions) from all continents were analyzed, particularly a large number of areas in countries belonging to the Global South, "which have the largest freshwater biodiversity reserves in the world, but which have been less studied or whose data is not known," explained Maria João Feio.

These countries include China, Nepal, Nigeria, Brazil, South Africa, Vietnam and Cambodia.

The research includes data from "areas considered biodiversity hotspots, such as the Amazon, and from countries such as Japan or South Korea, which until now were not accessible to the international community".

They also analyzed "the influence of human development and anthropogenic changes on the biological quality of rivers", which Maria João Feio said was "essential to understand what measures should be implemented at a global level".

According to the scientist, of the factors studied, the ones that most negatively influence rivers are the "poor physical and chemical quality of the water (a reality especially in Africa, Asia and South America), the fact that there are fewer protected areas for rivers and a higher level of human development, which can translate into a greater history of changes in land use by agriculture, industry and urbanization".

The factors associated with the better biological quality of rivers are an increase in the area of forest and better water quality.

As far as developing countries are concerned, they have "the highest percentages of moderately impacted sites, which may indicate a recent trend towards their degradation".

The study also showed that fish communities are in worse condition than invertebrate communities.

"In Australia's great Murray-Darling basin, 56% of the sites are severely altered, which may be due to the effect of the four thousand barriers to their movement along the river, such as dams or weirs. These are widespread in the world's rivers, as around 63% of the major rivers no longer flow freely," explained the researcher.

In his opinion, "this is particularly relevant when we know that a large number of new hydroelectric projects are being planned for South America and Asia".

For Maria João Feio, the study's conclusions reflect the "loss of biodiversity in freshwaters, as well as the change in species distribution patterns", with a growing increase in invasive species.

"All this alters the functioning of riparian ecosystems, leading to the loss of services provided by these ecosystems to populations (from water supply to climate regulation or disease prevention)."

In this context, he argued that it is essential to continue monitoring rivers around the world, "from those where nothing has ever been done to others that have seen their programs suspended", and to "plan recovery measures".

"Our study shows that establishing protected areas for rivers or improving forests are efficient solutions," he said. (RTP)